Thumb curling and index finger

[Lysistrata]

I've just been reading the New Scientist book 'How To Fossilise Your Hamster' (the 'home experiments' one) and it says that around 20% of people can't curl their thumb without their index finger bending inwards/downwards.

I immediately tried it and found that this happens with my right hand, but not at all with my left; does anyone know why? I'm right-handed if this has any relevance.

[mattie]

I am right handed, and I am the same as you, I can do it with my left hand, but not with the right.
However, if I push my right thumb instead of trying to move it on its own, my other fingers on my right hand stay straight.

I thought it had something to do with using a mouse all the time, put your hand on your mouse and see what shape it ends up in.

[Lysistrata]

I assume you use the mouse with your right hand? Mine doesn't do anything special on the mouse.
I was wondering if my years playing the cello had anything to do with it, or if it was natural and just helped with my playing (the left index finger needs to be much more independent than the right, which almost requires thumb curled, index finger down to sit on the bow).

[mattie]

I do use my right hand, but I work in IT and have been using a mouse every day for the last 10+ years, and my right hand stays slightly curled all the time - a sort of RSI, I suppose.

[ll_billym]

I'm left handed and my finger curls with the left hand but not the right.

I think it may be to do with holding a pen also, it's almost the same action.

[Lysistrata]

Would be interesting to see what happens with small children who haven't yet learned to write, use a mouse or play an instrument. I started the cello at 4 and presumably writing around the same time, so it's possible these actions influenced muscle/tendon development.

Anyone out there have it happen with both hands?

[4candles]

I'm right-handed, and the bending doesn't occur with either hand. My musical instrument is an electrocic keyboard if that's relevant.

[Robb Phoenix]

I'm right handed but i cant do it with my left hand but I can manage it with some stress on the right.

[doglady]

I never noticed this happening!! It happens on both of my hands.